Recently, as the portability and codeless tendency of instrument have progressed, a demand for a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery which is small in size and light in weight and has a high energy density, has been increasingly high. As a cathode active material for the non-aqueous electrolyte secondary battery, a composite oxide of lithium and a transition metal or the like (which may be referred to as a “lithium-containing composite oxide”) such as LiCoO2, LiNi1/3Co1/3Mn1/3O2, LiNiO2, LiNi0.8Co0.2O2, LiMn2O4 or LiMnO2, has been known.
Particularly, a lithium secondary battery using LiCoO2 as a cathode active material and using a lithium alloy or carbon such as graphite or carbon fiber as a negative electrode, can obtain a high voltage at a level of 4 V, whereby it has been widely used as a battery having a high energy density.
However, in the case of the non-aqueous type secondary battery using LiCoO2 as a cathode active material, further improvement has been desired e.g. in the discharge capacity, in the stability against heat during heating (which may be referred to as a “safety” in the present invention) and in the capacity density per unit volume of the positive electrode layer (which may be referred to as a “volume capacity density” in the present invention), and it had a problem of e.g. deterioration in the durability for charge and discharge cycles such as a gradual decrease in the discharge capacity of the battery by carrying out charge and discharge cycles repeatedly.
In order to solve these problems, various studies have been made. For example, it has been proposed to prepare lithium cobalt oxide having titanium oxide or lithium titanium composite oxide attached to the particle surface, by mixing preliminarily prepared lithium cobalt oxide with titanium oxide or lithium titanium composite oxide and firing the mixture (Patent Document 1).
Further, it has been proposed to prepare lithium cobalt oxide, by adding lithium hydroxide and titanium tetrachloride to a solution having preliminarily prepared lithium cobalt oxide dispersed, followed by heat treatment, so that a lithium titanium composite oxide be present on the particle surface (Patent Document 2).
Further, it has been proposed to prepare a lithium/manganese-containing composite oxide by adding lithium nitrate and a nitrate of a metal to a suspension having a lithium/manganese-containing composite oxide represented by Li1.1Mn1.9O4 dispersed, followed by stirring, dehydration and firing, so that the particle surface be covered with LiAlTiO4 having a spinel structure (Patent Document 3).